Mould and damp in loft

[Chris9953]

Hi all

I have recently moved into a 1950s house, due to sulphur contamination all the ground floors were replaced with solid concrete floors. I have also fitted central heating system upstairs as well as re plastering several rooms.

Now I have large amounts of mould, dripping water from the beams in the loft. There is no obvious leaks so it's condensation and it has only appeared in the last 4weeks. The floors were done. 9 weeks ago central heating 5weeks ago and rooms plastered 4 weeks ago.

The loft hatch as a good seal, I have moved the loft insulation further away from the rafters in the loft, it wasn't particularity close in the first place. There is no vents in the soffits and no obvious purpose ventilation I have made extra vents in the loft using my own version of those easy vents.

The insulation was there prior to me carrying out all this work. Now I think it's the water from the concrete, plaster and combined with the central heating the ventilation in the loft hasn't been sufficient.

Any thoughts please

[/list]

 

[footprints]

You might be wise to check the flue from the boiler looks intact if it passes through the loft just in case it is leaking.

Goes without saying don't tamper with it at all!

If it looks at all dodgy turn off and call the installer.

 

[wrightwoodwork]

I think you're on the right thinking of there being no ventilation in the attic causing the problem as the roof has no ventilation and with the new heating the warm air rises and so does the moisture and evaporates out through the vents. Which unfortunately are not present in your case and also your roof will have traditional roof felt and moisture can not evaporate through. So when the moisture become to heavy in the air it falls back down causing the condensation. It can be fixed by simply fixing some slate vents near the bottom and at the ridge or maybe round soffit vents in the eaves. Then the air rushes in at the bottom and out through the top taking with it the moist air and taking the condensation away. Also does the ceiling have a VCL as it should not the air moisture has to be allowed to evaporate through it by diffusion

 

[JohnD]

//www.diynot.com/forums/viewtopic.php?t=160032

 

[Perry525]

You have put one hell of a lot of water into your home, probably at a time when you have been keeping the windows closed to keep warm.

Gradually that concrete and plaster has been (and will be for some months) drying into the air.
Concrete dries at a rate of about one millimeter a day at a temperature of 70F degrees. You have some time to go?

In the normal way you would have the windows open, and over time the water vapour would disappear into the dryer colder air outside.

The water vapour is programmed by nature to head for the nearest cold surface/area, usually a cold window, but it is also rising into the cold loft.

Plasterboard is transparent to water vapour! Typically one and a half litres of water vapour can pass through a 8 x 4 foot sheet of plasterboard in 24 hours.(without making it wet)

The molecules of water vapour are incredibly small, they can pass through most things used in building - the condensation in the loft will disappear in time as your home dries. Just ignore it, once the warm weather comes the wood will dry back to what is normal in your area.

 

[wrightwoodwork]

A little bit unconventional but might help is to put a heater in the loft temporally and by doing so raise raise the moisture due point and remove the condensation from forming. On a cold day when we breath we all see the moisture from our breaths but on a hot day we can not see the moisture from our breaths. We simply can't see it on a warm say because the warm air is able to hold more moisture in the air, where on a cold day the air is unable to hold the moisture causing water vapour to form and condensation maybe just help as as a temporary solution

 

[Perry525]

A little bit unconventional but might help is to put a heater in the loft temporally and by doing so raise raise the moisture due point and remove the condensation from forming. On a cold day when we breath we all see the moisture from our breaths but on a hot day we can not see the moisture from our breaths. We simply can't see it on a warm say because the warm air is able to hold more moisture in the air, where on a cold day the air is unable to hold the moisture causing water vapour to form and condensation maybe just help as as a temporary solution

Sorry, you miss the point of it all!
It is because the air is warmer than the roof, that it holds water vapour.
But, on contact with the roof, the air cools and has to drop its excess water vapour; ie ;Condensation. Heating the air, will enable it to hold more water vapour, but the water vapour will still rush to the cold roof surface to condense. Water vapour is programmed by nature to move through the air towards the nearest cold surface or area. Think dew on the grass or frost! Cold ground attracts warm wet air, result dew or frost.

 

[wrightwoodwork]

Skip to content. | Skip to navigation

Sections
home courses about ocw help want credit?
Course
Wildland Fire Management and Planning Home
About the Professor
Schedule
Field Guide
Vocabulary
 
Personal tools
 
You are here: Home → Wildland Resources → Wildland Fire Management and Planning → Unit 4: Temperature-Moisture Relationship
Unit 4: Temperature-Moisture Relationship
Document Actions

Temperature & Heat   ::   Temperature & Altitude   ::   Atmospheric Moisture   ::   Relative Humidity   ::   Clouds   ::   Exercises

Atmospheric Moisture
You should realize that moisture in the atmosphere can appear in three states--solid, liquid, and a gaseous vapor. It is very rare when the air does not contain some water vapor. When the air is cooled to its saturation point, condensation occurs in the form of clouds and perhaps precipitation. At very high altitudes where the air is very cold, clouds consist of tiny ice crystals. And, of course, precipitation can occur in the form of snow and hail.


Natural forms of moisture in the atmosphere

An important point to remember is that each time water changes state it either gives off or takes on heat energy. When ice melts it requires about 144 BTUs of heat to change 1 pound of ice to water with a temperature of 32°. This is called the heat of fusion. It takes additional heat to raise the temperature of the water to reach its boiling point. This is about 180 BTUs for 1 pound of water. To change the liquid state into water vapor, it requires an additional 972 BTUs per pound of water. By changing state twice; that is, ice to water to vapor, approximately 1,300 BTUs of heat energy per pound of water has been stored in the moisture which is bound to the air. Any time condensation and freezing occurs, that amount of heat energy will be released, thus raising the temperature of the air.

It is possible in the atmosphere for ice crystals to go directly into water vapor, or water vapor directly to ice crystals. This process is called sublimation. The amount of heat involved in sublimation equals the sum of the heat of fusion plus the latent heat of vaporization.


Energy requirements to convert ice to liquid and liquid to vapor

When discussing moisture in the atmosphere, it's desirable to have some points of reference or means of qualifying the amounts present at any one time or place. The two most common points of reference used are dew point and relative humidity.

Dew Point : The temperature to which a parcel of air must be cooled to reach its saturation point.

A dew point is a useful reference because it tells at which temperature clouds and precipitation will occur. Does dew point change with changes in temperature or relative humidity? First, you should understand that the temperature of the air influences the amount of water vapor that can be bound to the molecules of air. Water vapor capacity increases with temperature increase. There are three parcels of air, each in separate containers. Only relative values of moisture and temperature are shown. At low temperatures, the air will hold only two parts of water vapor. As the temperature increases, it will hold 6, then 12 parts of water vapor. If the very warm air on the right is cooled, it must lose some of its bound water vapor. This will occur through condensation.

In any one stationary parcel of air, the dew point of that air will remain the same as will the amount of moisture in that parcel, regardless of air temperature. But as air temperature increases, so will the capacity of that air to hold more water vapor. The higher the air temperature, the stronger the bond between water and air molecules, and the drier the air seems to be.

To determine how dry or wet the air is at any given temperature, we use a unit of measure called relative humidity.

Relative Humidity : The ratio of the actual amount of water vapor in a given volume of air to the amount which could be present if the air were saturated at the same temperature. It's commonly expressed as a percentage.

Since warm air will hold more moisture than cold air, the percentage of relative humidity must change with changes in air temperature. The graphic below illustrates this relationship. Again we have three parcels or containers of air. The number of water vapor molecules is the same in each container. At 40° air temperature, the parcel is saturated and will hold no more molecules of water vapor. The relative humidity is 100 percent. If the temperature of that air parcel is raised by 20°, it will hold about twice as many water molecules to reach saturation. Thus, the new relative humidity is now 48 percent. If the temperature is raised another 20°, it will again double its capacity to hold water vapor molecules. The relative humidity is only 24 percent.


Relative humidity decreases as temperature increases

The importance of air temperature to moisture is obvious. At 80°, the air has a relatively low humidity and is relatively dry. As it cools, the humidity increases, reaching its saturation point at 40°. Now the air is very moist, and clouds will form. The dew point of the air is 40° in all three containers in the illustration.

The example in the graphic below shows a relatively moist airmass with a dew point of 60°. A relatively dry airmass has a dew point of 38°. This illustration shows that a cool, dry airmass may actually have a higher relative humidity than a warm, moist airmass. Relative humidity alone can be misleading when comparing atmospheric moisture conditions.


A cool, dry air mass may actually have a higher relative humidity than a warm, moist air mass.

Rule of Thumb : Relative humidity doubles with each 20 degree (Fahrenheit) decrease, or halves with each 20 degree increase in temperature.

Generally, as temperature goes up, relative humidity goes down and vice versa.

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . This work is licensed under a Creative Commons License
 
:: site map :: accessibility :: terms of use :: privacy policy :: hosted by :: supported by
Powered by eduCommons Valid XHTML Valid CSS Section 508 WCAG

 

[JohnD]

were you trying to make a point?

what was it?

 

[wrightwoodwork]

The point is that moisture content is relative to air temperate and obviously when hot air touches a cold surface moisture forms Obviously the best way is ventilation

 

[Perry525]

The point is that moisture content is relative to air temperate and obviously when hot air touches a cold surface moisture forms Obviously the best way is ventilation

While prior to the 1970's oil shortages that was true.

Since then we have had the IPEC agreement where
lower oil use results in higher costs. And our Power
companies are working to the same principal, use
less pay more.

Adding ventilation to a roof increases heating and
cooling costs, as the passing wind creates an area
of low pressure to the lee and above the roof, as it
tries to lift the roof off. This results in air being
pulled from the roof (as you describe as ideal) which
at the same time pulls our heat from the home!

This heat is replaced by cold air, that then has to heated
at great cost to the home owner.

As we are continually being urged to wear an extra
jumper, turn our heating down, add more insulation.
Ventilating our roofs and increasing our running
costs is not good advice.

 

[wrightwoodwork]

Adding ventilation to a roof increases heating and
cooling costs, as the passing wind creates an area
of low pressure to the lee and above the roof, as it
tries to lift the roof off. This results in air being
pulled from the roof (as you describe as ideal) which
at the same time pulls our heat from the home!

I'm going to disagree with that statement I'm not saying it's wrong but it is only correct when the ventalation is not carried out correctly and the ceiling is not 100% air tight
Dr. Joseph Lstiburek talks about the not-so-controversial ways to maximize the efficiency and airflow of your roof and attic.
Video Transcript:
There’s been so much stuff said about roofs that you sometimes lose perspective. I’m going to start off by saying what might seem controversial but really shouldn’t be.
This is a vented attic, and it’s probably one of the most unappreciated building assemblies we have in the history of building science. It’s beautiful. It’s hard to screw this up.
For 20% of the effort, it gets us to 80% of optimal performance, and it works in hot climates, in mixed climates, the Arctic, the Antarctic, the Amazonian rain forest — it works absolutely everywhere. The value proposition of a vented attic, meaning the money that you invest in building one of them — it’s hard to argue with the benefits. But for all kinds of reasons, we manage to screw it up.
The single most important thing you have to remember about a vented attic is that the ceiling plane — the gypsum board layer, the drywall layer — needs to be airtight.
1) The ceiling plane MUST be airtight
Absolutely airtight. Above the airtight ceiling plane, the only thing that should be seen is insulation and air, nothing else. Not last year’s Christmas decorations, not your high school prom dress, not the tuxedo you were married in and can no longer fit in. Nothing but lots of insulation and air. Just an airtight ceiling and nothing else.
2) If you’re going to vent the roof, then VENT THE ROOF
If you’re actually going to vent the roof, let’s be serious about venting the roof. Wash the underside of the roof deck with air. That means the entire perimeter of the roof needs to have air inlets, meaning continuous soffit ventilation. It’s dumb to have baffles every third or fourth bay, the entire underside of the roof deck should be washed. Where the air leaves isn’t as important — whether it’s a ridge vent, or mushroom caps, or gables. What’s important is that you have continuous air entry at the perimeter of the roof down low.
3) Put more vents down low than up high
This is where the code tends to have it wrong. You want more entry points at the perimeter than exit points at the top.
People say you want to balance the lower down ventilation with the upper ventilation, and a lot of people interpret the codes to say that if you get it unbalanced you want more ventilation up high. That is absolutely wrong; you don’t want more places for the air to get out than to get in. The reason is, if you construct a house with a leaky attic ceiling and you have lots of ridge vents or you have lots of vents up high, the makeup air is going to be pulled from the house rather than being pulled from the outside. That scenario is a disaster.
Attics should be ventilated with air from the outside, not the inside. That’s why I hate these whirligig turbine vents — because they depressurize the attic, and if your attic ceiling isn’t perfectly airtight, you suck air conditioned air or heated air out of the house.
It’s even crazier when the powered attic fans can actually suck on the roof and they’re controlled by a thermostat. How stupid is that? Of course the attic is going to be hot. You turn them on and they suck all the air conditioned air out.
No powered attic ventilation; more vents down low than up high; wash the entire underside of the roof deck. But all of that is secondary to having the ceiling plane airtight.
This last tip is more important in cold climates than anywhere else. But where the ceiling insulation hits the perimeter wall, you don’t want the amount of ceiling insulation on the top plate to ever be less than the R-value in the wall itself.
4) Put more insulation on top of the wall than inside it.
In other words, if you have an R-20 wall, you want at least R-20 on your top plate. A higher R-value is better, but a lower R-value is not. If you have an R-30 wall you want at least R-30 on top of your top plate.
A reasonable rule of thumb is: Thou shalt never, according to Joe’s Rule of Thumb, have less R-value on the top of your top plate than in the wall. It would be nice to have even more, but not less.
Notice: nowhere in this discussion did the term “vapor barrier” come up. If you really want to have a vapor barrier in the ceiling, limit it to climate zone 6 or higher, but that’s really not important compared to the airtightness of that ceiling plane.
The building code calls for a vapor retarder in climate zone 6 or higher. It’s okay to put one in, but if you don’t, take a Valium and relax. You don’t want to go through a lot of brain damage in a renovated house to try and add a vapor barrier underneath insulation in an attic. What you really want to do is make that ceiling plane airtight, make it airtight, declare victory and be done. Don’t mess around with permeability’s and calculations and whatever.
To recap, airtightness on the ceiling; washing the underside of the roof deck; unbalanced ventilation should be in favor of the lower vents because you don’t want to depressurize the attic; no to powered attic ventilation or the whirligigs; and you don’t want to squeeze the insulation at the perimeter so it’s less than the R-value of the wall.
That’s it. You can build that everywhere in the world and life is good.

What do you suggest to improve the situation

 

[JohnD]

prior to the 1970's oil shortages that was true.

Prior to the 1970's house insulation was woeful.

A house meeting modern insulation standards will have 270mm of loft insulation. The amount of heat that gets into the loft is so small that it is of no consequence that the loft is well ventilated. Heat loss is still far far far less than in your 1970's house.

Ventilating our roofs ... is not good advice.

Yes it is.

 

[hughesman]

Hello

Is it normal for a brand new house to develop mould in the loft space?

I moved into a brand new hi-spec house in August 2013, there are signs of mould in the loft on plastic storage boxes I put up there about a month ago. I put a moisture trap up there two weeks ago and there is about 1/3 of a cup of water in it.

The builder suggested I should be wary of storing anything in the loft when I moved in for this reason and said it was normal for modern houses to have this issue?- is that true?

If the house meets building regs- what can i do?

 

[wrightwoodwork]

It is something that seems to be seen more and more but that does not mean you should be seeing it. Do you need to store plastic boxes in the attic the mould needs to be treated a mould treatment to kill the bacteria following the manufacturer instructions. It can't be just hovered and wiped down as it will on spread the spores else where not killing them. A plastic box in a state of the art house attic is still a plastic box. As it is plastic it is not hygroscopic ( think that's the right word)and does not take up moisture where a cardboard box or wood box will. If you kill the mould it will hopefully sort the problem, look at storing the plastic boxes elsewhere if practical check insulation is not touching the roof felt. Also check that there is no stray plastic bags under the insulation acting as a vapour barrier. Check at the eaves for ventilation If it is covered make sure it is not covered. If you can't see any ventilation don't worry about it your roof will have a product on it like tyvek which does not need roof ventalation as it allows water vapour to pass through it